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Патент USA US2105666

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Jan“ 18,1938.
E. D. LILJA
$2,105,666
SYNCHRONOUS MOTOR
Original Filed Jan. 13, 1953
HIGHER
UNIT, , » "
RESIST/WT!’
,
L3 1
3/
,
INVENTDR
‘Ea/gar’ D‘ L £110
BY
'
.
TTQRNEY§
Patented Jan. 18, 1938
I
_ ,
UNITED STATES PATENT OFFICE,
SYNCHRONOUS MOTOR
Edgar D. Lilia, Rockford, Ill., assignor to Howard
D. Colman, Rockford, Ill.
Continuation of application Serial No. 651,515,\
January 13, 1933. This application April 6,
1935, Serial N0. 15,042
26 Claims. (Cl. 172-478)
My invention relates to small synchronous al- a high ?ux density in all parts of the stator iron.
ternating current motors adapted to operate at
r
The winding 6 is adapted to beenergized from a
a sub-synchronous speed and has more particu-
single phase source of alternating current such
lar reference to a motor of this character in
as a household lighting circuit.
0 which shifting of the magnetic field is produced
by the action of shading rings.
The primary object of the present invention is
to provide a sub-synchronous motor which will
start and pull into synchronism under a load sub-
0 stantially greater than motors of similar character heretofore used.
'
r above character in a manner such as to produce
1" a reaction torque therebetween tending to establish a comparatively high sub-synchronous speed,
and produce strong induction motor action not
only for initiating rotation of‘ the motor but
also to augment the reaction torque whereby to
20 produce a substantially higher power output than
could be had in prior sub-synchronous motors.
The invention also resides in the novel manner
by which the strong synchronous characteristics
are obtained.
_
A further object is to construct the stator in
a manner such as to prevent the rotor from overrunning its established synchronous speed under
the induction motor action developed.
Other objects and advantages of the invention
30 will become apparent from the following detailed
description, taken in connection with the accom
panying drawing, in which
.
-
-
plates I01’ rigidly secured at opposite ends to the 10
The primary and secondary
members are relatively rotatable, the primary
member being preferably ?xed in order to avoid
the use of slip ring connections 01‘ the like in the
supply circuit of the energizing winding
Shifting of the magnetic field around the rotor
It! is produced by the well known action of shad
ing or short-circuited rings enclosing side por-»
tions of the pole pieces adjacent the rotor. For
a purpose to later appear, the poles of opposite 20
sign are differentially or unequally shaded in the
present instance, there being two rings H and
II on the D018 Piece 8 and one ring l3 0n the
pole piece 9.
The rings II and I3 enclose ap
proximately one-third of the respective pole 860- 26
tions and, for the size of motor shown, have re
sistances within a range of approximately 1 to
2X 10-‘ Ohms. Preferably, the ring ll 15 formed
from No. 8 B. 8; S. gauge copper wire while the
ring I3 is made from No. 10 wire. The large!‘ 30
ring-l2 may be of the same size wire as the ring
H, enclosing the same vsectional area and an
Figure 1 is a perspective view of a motor embodying the features of the present invention,
35 va portion of one of the bearings being broken
away-
latter is fast on a shaft Ill"- Journaled at oppo
site ends of the rotor in bearings supported by
?eld member 5.
Another object is to coordinate the construction of the stator and rotor in a motor of the
The other side
of the ?eld member de?nes two pole pieces 8 and 6
9 with opposed faces de?ning arecess in which
a. rotor or secondary member In is disposed. The
I
adjacent section preferably not greater thanthat
enclosed by the ring H.
.
With the shading rings arranged as above 1'18- 35
scribed, the face of pole piece 8 is divided into’
Fig. 2 is an elevational view of the motor shown
in Fig. 1, the rotor being shown in section.
Fig. 3 is a perspective view of the rotor.
40
Fig. 4 is a fragmentary view of a portion of
Fig. 2 showing the rotor in a different position?
Fig. 5 is a view of a four pole motor constructed
in accordance with the present invention.
unshaded, single shaded and double shaded areas
l4, l5, and I6 which are separated by slots l1 and/
Hi and in which the magnetic flux reaches its
peak value successively, producing a gradual 40
shifting of the magnetic field in a ‘clockwise di
rection as viewed in Fig. 2. The face of ‘the pole
8 is divided by the slot l‘lb into unshaded and
_ ' Fig. 6 is a view similar to Fig. 4 illustrating a
4" modi?cation.
'
In the exemplary embodiment shown in Figs.
1 to 4, the motor is constructed with a stator or
primary member of the two pole core type com-
shaded areas l8 and I9, and for, this reason, a
less progressive shifting of the field takes place 45
across the face of this pole. Also the shading '
eifect of the ring I! is less than that of the rings
II and I2. .As a result of this differential or uni
prising a rectangularly shaped laminated field
equal shading of the two poles, the magnetic
member 5 approximately two and ?ve-elghths
inches long, ‘two inches wide and ?ve-eighths
inches thick. A main winding 6 providing a magneto-motive force of approximately 500 ampere
field does not shift uniformly across the faces 50
of the two poles. In view of the low resistance
of the shading rings H and I3, each of the stator
poles is heavily shaded as a result of which the
turns encloses one side leg 1 of the member 5 and
?ux threading the rotor from the shaded areas
when excited with alternating current produces
attains a maximum value approximately sixty 55
.
2
2,105,666
electrical degrees later than does the flux from
the unshaded areas.
tends to revolve synchronously at 2400 R. P. M.
in the magnetic ?eld created by the two pole
To enable a powerful induction motor action
stator when the latter is excited from a 60 cycle
and strong synchronous characteristics to be ob
tained, .the ?eld member 5 is constructed with
extensions 20 and 2| of the unshaded side tips
of the pole pieces 8 and 9, which extensions pro
vide magnetic connections between the adjacent
side tips of the poles. These extensions are un
interrupted at least up to the median plane be
tween the adjacent poles by any nonmagnetic
restriction greater in magnetic effect than an air
gap 311 of an inch wide. In the present instance,
each unshaded side tip is integrally joined to
15 the shaded side tip of the pole of opposite sign.
In the case of the pole piece 8, the unshaded tip
source. This speed is maintained primarily by
the action of the unshaded areas of the two poles
8 and 9 acting as separate magnetic poles which
become strongly polarizedeach time the unshaded
?ux rises to its peak value which occurs 7200
extension 20 thereof is interrupted, for a pur
pose to appear later, by a magnetic restriction
hi the form of a hole 2i!‘l preferably located about
20 midway between the poles. The continuous inner
surfaces of the extensions which closely follow the
rotor surface constitute enlargements of the un
shaded pole areas l4 and i8, thereby rendering
additional iron of the rotor available for the en
try of the unshaded flux.
If a ‘bi-polar synchronous rotor were used in
times a minute. In each polarization, an at
tractive force is exerted on the rotor poles then
positioned nearest the unshaded pole areas, the
greatest attraction occurring when the unshaded
?ux reaches its peak value with the rotor posi
tioned as shown in Fig. 2, with one pole 23 di
rectly opposite the unshaded area l4 and the ad
jacent air gap opposite the single shaded area l5.
Another rotor pole will then be positioned directly
opposite the unshaded face area H of the pole
piece 9 and adjacent the shading ring slot l‘lb
while the third rotor pole will be disposed opposite 20
the double shaded area Ii and the extreme end of
the extension 21 of the pole 9.
With the rotor positioned relative to the stator
poles as above described, it will be apparent that
the unshaded ?ux will thread the rotor along a
path represented by lines 21 which separate at
the rotor pole opposite the area i4 and then ex
the rotating ?eld produced when the two pole
stator above described is energized by ordinary
60 cycle alternating current, such a rotor would
tend through the other two poles. The path thus
30 revolve at the same speed as the ?eld, that is,
sence 01' an air gap of appreciable width therein
or the inclusion therein of any of the stator iron
provided is of low reluctance owing to the ab
3600 R. P. M. The present motor is constructed
to possess strong synchronous characteristics at enclosed by shading rings. Moreover, the slots
l7, l1‘, and l‘lb and the hole 20“ are so spaced
the same time establishing a synchronous operat
as to effectually avoid diversion of any substan
-ing speed substantially below the natural syn
chronous speed determined by the number of tial amount or unshaded ?ux out of the desired "
path through the rotor, the slot HE‘ and the hole
stator poles. To this end, the rotor I0 is com
posed of magnetizable material of low magnetic 20'- being so spaced as to confine the unshaded
retentivity such as highly permeable iron and' ?ux of one stator pole to an area H which spans
comprises a core 22 from which extend equally only one of the rotor pole projections. Substan
spaced solid laminated projections 23 greater in tially all of the available unshaded ?ux will thus .40
number than the number of stator poles and con
stituting salient poles. Thus, if there are N poles
on the stator, N+M poles 'are used on the rotor
so that a well defined subsynchronous operating
speed is had which is a fraction of the theoretical
or true synchronous speed of the motor as deter
mined by the number of stator poles. In gen
eral, one rotor projection advances past a pre
determined point on one unshaded pole section of
50 the stator for each half cycle of the energizing
current.
The number of rotor poles is preferably close
to the number of stator poles so that a high
sub-synchronous speed will be had. In addi
55 tion, an odd number of rotor poles is preferably
used for each pair of stator poles. Thus, in the
present instance, there are three rotor poles for
each pair of stator poles of opposite sign and each
rotor pole is formed with sides disposed substan
60 tially radially including a polar arc at least equal
to one-fourth of the rotor pole pitch‘ and pref
erably of approximately sixty degrees where a
three pole rotor and two pole stator are used and
optimum synchronous characteristics are desired.
65 The adjacent poles 23 thus define a segmental air
gap the circumferential length of which is the
same as that of the poles 23 and slightly greater
than that of the single shaded area I! of the
pole piece 8.
70
For reasons to appear later, best results are
obtained when the poles are of a height approx
imately one-half of the rotor radius, being ?ve
thirty~seconds of an inch for the present rotor,
the diameter of which is 0.664 inch.
The rotor constructed with three salient poles
be utilized in causing a strong attractive force
to be exerted on the rotor pole, under the area
14 when it is in the position shown in Fig. 2.
From a comparison of Figs. 2 and 4 and con
sideration of the intervening positions which the
rotor may occupy, it will be apparent that there
is only one position (Fig. 2) which is favorable
to the attraction of a rotor pole with a force of
substantial ,magnitude. With the rotor posi
tioned as shown in Fig. 4, the reluctance of the
magnetic path through the rotor and the un
shaded pole areas is a maximum owing to the
fact that one non-magnetic segment of the rotor
is disposed opposite the unshaded area l4 and
diversion of flux from such area and around the '
rotor is effectually reduced by the hole 20‘ and
the adjacent slot H. In addition, the shaded
flux is, owing to the heavy shading of the poles
as above described, so reduced in magnitude that
no appreciable locking action is produced there
by. The reluctance oi’ the path through the un
shaded areas decreases progressively as the rotor
moves from the position shown in Fig. '4 to the
synchronous position of Fig. 2 and increases to a
maximum as the next non-magnetic-rotor seg
ment is presented to the area. 14. It follows
therefore that only the unshaded ?ux is of sun‘!
cient strength to produce the desired locking ac
tion on the rotor and there is only one positional
relation of the stator and rotor poles which is
of su?lciently low reluctance to cause strong at
traction of the rotor poles by this ?ux. This will
be apparent from a consideration of the positions
of the rotor projections or magnetic segments
with relation to the pole pieces on the stator.
60
2,105,666 1
3 ,
‘ Thus, the unshaded portion of the lower stator
projection 9 is of major-extent and covers ap
ing from the use of the extensions 20 and 2|, a
or the length of three of the minor-extent pe
though the amount of available rotor iron is de
creased considerably as a result of forming the
rotor with salient poles and intervening non
comparatively high torque is developed to initiate
proximately 180 degrees of the rotor periphery . rotation of the rotor, in the present instance, even
ripheral segments thereof. Consequently, the
reluctance of the magnetic path between this
unshaded portion of the stator pole 9 and the
rotor varies less than 50. per cent during rota
tion of the rotor. The face M of the unshaded
10 portion of the upper pole 8, however, covers only
one of the minor~extent segments of the rotor
and consequently, the reluctance of the magnetic
path between the rotor and the face or pole piece
I4 varies approximately 100 per cent during ro
tation of the rotor. In general, then, the stator
or primary member is provided with one pole
piece having an unshaded portion of major—ex—
tent which cooperates with the rotor portion to
form a ?ux path varying less than 50 per cent
from its maximum value of reluctance while a
second pole piece has‘ an unshaded portion form—
ing a flux path that varies approximately 100
per cent in reluctance thus exerting a strong
synchronizing effect on the rotor.
25
The synchronous position (Fig. 2) above re
ferred to is de?ned accurately owing to the fact
that the rotor poles and the intervening non~
magnetic gaps are of equal circumferential length
substantially equal to the distance measured cir
cumferentially between the hole 20a and the slot
I ‘I and also the distance between the slots l1 and
'
As a true induction motor, when excited from
a 6G cycle source, the present motor has a theo
retical synchronous speed of 3600 R. P. M., the 10
speed of rotation of the magnetic ?eld, but owing
to slippage between the rotor and the ?eld, the
actual speed at which the rotor tends to run
under the torque developed by the induction mo
tor action alone is substantially less than 3600 15
R. P. M. yet greater than that established by the
synchronous character of the rotor. In fact,
with the stator and rotor constructed as above
described, the "most efficient induction motor
speed is very near 2400 R. P. M., that is to say, 20
the product of the speed and torque has a theo
retical maximum at this speed. It will be ap
parent. therefore, that the full effect of the torque
due to the induction motor action is exerted not
only during self-starting of the rotor but also in 25
accelerating the rotor all the way up to the es
tablished sub-synchronous speed, since as was
before noted the sub-synchronous~ speed is also,
2400 R. P. M. for this motor. The term “theo
retical maximum” has been used since it is ap
30
rotor is thus de?ned accurately.
parent that the actual maximum is determined by
the sub-synchronous speed. In other words, the
sub-synchronous speed might be so low that the
rotor would be locked into step at this low speed
long before it had attained the speed commen
surate with the theoretically most ei?cient induc
tion operation. The present motor relates these
speeds in such manner that the strong induction
characteristics are fully utilized.
The factors above described combine effectu
ally to cause powerful attractive forces to be ex
In addition, with a rotor of the above charac 40
ter operating in the stator described, a very
i1“. With this arrangement, it will be apparent
that the reluctance of the path 21, which is a
minimum with the rotor positioned as shown in
Q; in Fig. 2,’ will increase rapidly as the rotor is shifted
in either direction, becoming a maximum when
the adjacent air gap comes opposite the area
14 as shown in Fig. 4. The locking position of the
49
magnetic segments.
‘ erted on the rotor poles when the rotor is locked
powerful starting torque is developed which is
in step with the pulsating stator ?eld. A power
ful torque is thus developed tending to prevent
the rotor from being pulled out of synchronism
capable not only of overcoming the torque tend
ing to lock the rotor in the position shown in Fig.
2, but also of exerting torque of substantial mag
under a load or over-running the established
nitude for initiating rotation of the rotor. As a
result, the motor will start and accelerate to the
established sub-synchronous speed under a load
substantially greater than the shaded pole mo
tors heretofore used. Moreover, in view of the 50
fact that the motor operates at the highest pos-_
sible sub-synchronous speed for a two pole stator,
a maximum power output of the motor is ob
tained. When the synchronous speed has once
been attained, the load may be increased sub—
stantially without pulling the motor out of syn
synchronous ‘speed under the induction motor
action later to be described.
To produce a torque for initiating operation of
the motor automatically and to augment the
torque due to the synchronous. characteristics
when the rotor is at synchronous speed, conduc
tors in which currents may be induced are
mounted on the rotor. Preferably, these conduc
tors form a squirrel cage for which the iron of
the rotor l0 forms a core. Herein, the squirrel
cage comprises disks 28 of copper at opposite
ends of the rotor electrically connecting corre
sponding ends of copper inductor bars 29 which
60 are disposed in the grooves de?ned by the adja
cent poles of the rotor. The inductor bars may
be of any desired cross-sectional shape, and for
best performance in the motor shown, the bars
should have a cross-sectional area equivalent to
The bars shown
C; Li No. 7, 8 or 9 B. 8: S. gauge wire.
herein are formed of No. 8 gauge wire. -
'
'With this squirrel cage rotor, the motor starts
as a result of the well known induction motor
action caused by reaction of the rotating mag
netic ?eld and the current induced in the
squirrel cage. Owing to the high flux densities ob
tained, the e?icient arrangement of the sharing
coils resulting in heavy shading and substantial
phase displacement, andthe manner 01' distribut
ing the unshaded flux to the rotor iron result
chronism. This powerful pull-out torque is due
to a combination of the induction motor action
and-“the synchronous motor action which latter
is attained as above described when the rotor is 60
revolving at or near synchronous speed.
In addition to their function of distributing
the unshaded ?ux so that the latter will act with
maximum effectiveness in producing a powerful
synchronous action, the extensions 20 and 2|
contribute to the development of the powerful
induction motor torque. This is due primarily
to the efficient maner in which the unshaded ?ux
is distributed to the rotor iron by enlargement of
the unshaded areas of the poles so that the av 70
erage amcuntlof unshaded ?ux passed through
the rotor during a cycle is the maximum con
sistent with the maintenance of de?nite maxi
mum and minimum flux positions. In this way,
the current induced in the squirrel cage winding 75
4
2,105,666
is increased and the induction motor torque ac
cordingly improved without impairing the ac
curacy with which the synchronous position of
the rotor relative to the unshaded pole areas is
de?ned.
By virtue of the induction motor action above
referred to, it will be apparent that the rotor,
when the motor is under a light load, tends to
over-run
its
established
synchronous
speed.
10 This tendency is counteracted by the synchronous
action above described, for the reason that strong
retarding impulses are exerted on the rotor poles
if the latter run ahead of the field and one is
disposed in advance of the position shown in Fig.
2 at the time when the unshaded flux reaches its
peak value. To further insure against such
over-run, the rotating magnetic ?eld is rendered
somewhat discontinuous in the present motor by
shading the stator poles differentially thereby re
clucing the induction motor action available for
carrying the rotor beyond synchronous speed.
This is attained by using only one shading ring
l3 on the pole piece 9 or by constructing this ring
to possess a weaker shading effect than the com
bined effect of the rings H and [2. As a result,
the pole 9 is rendered less effective than the dou
40 integral with the unshaded side tips of the
poles 33 and the shaded side tips of the
poles 32 form similar enlargements of the un
shaded area of the former poles.
Holes 40‘ are
formed at the'center of the extensions 00.
The rotor or secondary member employed is
mounted on a shaft 4| \journaled at opposite ends
in bearing plates (not shown) secured to the pro
jections 32 and 33. To obtain the desired syn
chronizing and induction motor characteristics, 10
the same as in the two pole motor above de
scribed, the rotor comprises a laminated substan
tially circular core 42 having salient poles 43 pro
jecting therefrom with their minor-extent faces
terminating adjacent the faces of the poles 32 and 16
33, the poles 32 having major-extent unshaded
pole faces thereon. The rotor carries a squirrel
cage formed by inductor bars 44 electrically
joined at corresponding ends by copper disks (not
shown).
As in the case of the two pole motor ?rst de
scribed, thé number of rotor poles 43 is greater
than the number of stator poles, there being six
poles in the present instance equally spaced apart
a distance slightly greater than the circumfer
25
ential length of the single shaded face area of the
poles 33. When the rotor is positioned as shown
ble shaded pole 8 causing the slippage necessary
to enable the established synchronous speed to be .in Fig. 5, a rotor pole will be disposed opposite
each of the unshaded face areas of the poles
maintained. Moreover, the dynamic braking ef
30 fect of the less heavily shaded pole is increased 33 and the adjacent pairs of rotor poles will be 30
which also contributes to the maintenance of the opposite the extensions 38 and double shaded
areas of the poles 33 and a magnetic path of low
synchronous speed.
It has been found that the height of the rotor reluctance as indicated by the lines 45 will be
poles 23 is of importance in maintenance of the
35 established synchronous speed. This is for the
reason that if these poles are made substantially
shorter than above described, the rotor would
more nearly resemble a true squirrel cage rotor
and its synchronous characteristics would be re
duced accordingly. By constructing the rotor
with poles of greater height than shown, the iron
adjacent the rotor shaft available for carrying
the flux would be reduced resulting in a reduc
tion in the amount of ?ux threading the rotor
45 and a corresponding reduction in the syn
chronous and induction motor torque.
The present invention may be embodied in
shading ring motors having more than two poles.
For example, Fig. 5 shows a motor having four
50 stator poles and a rotor constructed to revolve at
1200 R. P. M. This motor has a field or primary
member comprising four annularly spaced pole
pieces arranged in pairs 32, 33 and connected by a
core 30 enclosed by a winding 3|.
When the
winding 3| is excited by single phase alternating
current, the adjacent pole pieces are oppositely
polarized while the alternate pieces are of the
same sign.
.
For the purposes above described in connection
60 with the motor shown in Fig. 2, the pole pieces
32 and 33 of each pair are differentially shaded,
there being two rings 34 and 35 on each of the
pole pieces 33 and one ring 36 on each of the pole
pieces 32, arranged in a manner similar to the
65 shading rings H, i2 and I3. Slots 3'! separating
the differently shaded sections are inclined rela
tive to radii of the rotor in order that the proper
spacing of the diiierently shaded sections of the
different poles may be obtained even though the
70 polar projections are not equally spaced.
The unshaded side tip of each pole 32 is in
tegrally joined to the shaded side tip of the adja
cent pole 33 by an extension 38 defining the root
of a V-shaped notch 33 in which one side of‘ the
75 shading rings 34 and 35 is disposed. Extensions
available for the unshaded flux.
Owing to its
strong synchronous characteristics, the rotor
tends to lock in step with the pulsations of the un
shaded ?eld, its successive poles moving into the
positions shown in Fig. 5 as the unshaded flux
reaches its peak values. Since the magnetic field
set up through the unshaded area of the poles 33 (0
attains a peak value 7200 times a minute with 60
cycle excitation, the rotor thus constructed will
turn at 1200 R. P. M. which is the established
synchronous speeed of the motor when connected
to a 60 cycle source of supply. As in the case of
the two pole motor described above, the stator
or primary member is provided with an unshaded
pole piece having a face of major-extent as com
pared to the minor-extent segments or projec
tions on the rotor and‘ which covers approxi
mately three of the rotor segments so that the re
60
luctance of the flux path from this unshaded por
tion of the pole piece to the rotor varies less than
50 per cent during rotation of the rotor. The
stator is also provided with an unshaded pole
piece which is approximately equal in length to
one of the segments of the rotor so that the re
luctance of the flux path from this latter pole
piece to the rotor varies approximately 100 per
cent upon rotation of the rotor, thus exercising
a strong synchronizing effect thereon.
It will be apparent that in the four pole motor,
the induction motor action contributes to the
pull-in torque in the same manner and that the
poles 32 and 33 are differentially shaded for the 65
same reason as in the two pole motor ?rst de
scribed.
Fig. 6 illustrates another modification substan
tially identical in construction to that shown in
Figs. 1 to 4, except that no holes are placed in 70
the pole extensions 20 and 2| and the differential
shading of the poles is obtained by the use of a
ring 46 on the pole 9 preferably enclosing a
greater sectional area of the pole and having
greater resistance than the ring H of the motor
5
2,105,000
first described. From a comparison of the va
rious embodiments illustrated it will be seen that
the desired unsymmetrical distribution of the un
shaded and shaded ?uxes or differential shading
may be had either by using shading rings on dif
ferent poles enclosing different areas of the pole
pieces or by augmenting the shading ?ux in cer-.
tain portions of the pole pieces with additional
shading rings. Preferably, the ring 48 has a re
10 sistance of approximately 7><l0—4 ohms and is
formed from No. 16 B. & S. gauge wire. In order
that there will be only one rotor position for each
pole ‘which is favorable to the production of a
strong attractive force, the ring KB preferably
encloses approximately two-thirds of the pole
piece 9. When the rotor is in the synchronous
position shown in Fig. 6, a path of low reluctance
‘indicated by the line 41 is available for the un
shaded ?ux. In this position, one of the rotor
poles is disposed opposite the shaded area is but -
threading of the unshaded flux through this pole
is opposed by the bucking action produced by the
currents induced in'therring 46. Thus the un»
shaded ?ux is confined effectually to the path
M and utilized most effectually in locking the
rotor in step with the pulsating ?eld. When the
rotor turns approximately 60 degrees from the
position shown in Fig. 6, it will be seen that the
reluctance of the ?ux path from the stator to the
rotor remains substantially constant on one side
of the rotor While it varies approximately 100
per cent on the other side thereof.
As a result, a
strong synchronizing e?c'ect is imposed on the
rotor.
It will he noted that in all of the motors shown
the shading rings are in each instance located on
what may conveniently be termed corresponding
portions of the pole pieces, that is, on the same
sides of the successive pole pieces although they
46 do in, some instances enclose portions of dilferent
cross-sectional area.
application Serial No. 651,515, ?ied January 13,
1933.
.
I claim as ‘my invention:
. l. A synchronous alternating current motor
combining a stator providing two opposed pole
pieces having faces de?ning a rotor recess\ap
proximately ?ve-eighths of an inch in diameter,
50 short-circuited rings on said pole pieces shading
corresponding side portions thereof, a rotor com
posed of, magnetizable material of low magnetic
retentivity and having a central core and three
salient pole projections extending therefrom to
on LA a point closely adjacent said stator pole faces, a
squirrel cage winding on said core, means pro—
viding magnetic paths of low reluctance adjacent
60
said rotor and between the shaded and unshaded
side tips of said stator pole projections, said rotor
pole projections being approximately ?ve thirty
seconds of an inch in height and each having an
end face including a polar arc of approximately
sixty degrees with intervening non-magnetic seg
mental gaps‘ of substantially equal circumferen
tial lengths.
_
ing a central core and a plurality of salient pole
projections extending therefrom with their faces
spaced apart a. distance substantially equal to
the spacing of the unshaded and most heavily 5
shaded areas of said?rst mentioned pole piece,
a short-cir-cuited winding on said rotor for caus
ing an induction motor torque to be created upon
energization of said stator, and a magnetic con
nection closely following the rotor contour and
interposed between the unshaded side, portion of
said second pole piece and the most heavily
shaded side portion of said ?rst mentioned pole
107
piece.
3. A synchronous alternating current motor 15
comprising, in combination, a stator having an
energizing winding and a plurality of annularly
spaced pole pieces having end faces de?ning a
rotor recess, a pair of shading rings on one of
said pieces dividing the pole section substantially
equally into an unshaded side section, an inter
mediate section shaded by one ring and a side:
section shaded by both of said rings, a single
shading. ring enclosing a portion of another of
said pieces on the corresponding side thereof, a 25
rotor composed of magnetizable material of low
magnetic retentivity and comprising a core hav
ing equally spaced salient projections greater in
number than the stator poles and spaced apart'a
distance substantially equal to the spacing of the 30
unshaded and double shaded face areas of said
first mentioned piece, and a conductor on said
rotor vin which currents are induced to produce
induction motor action.
4. A synchronous alternating current motor 3d
combining a stator having an energizing winding
and providing a plurality of annularly spaced -
pole pieces, a short-circuited ring enclosing a
side portion of one of said pole pieces and shad
ing a major portion of the pole piece section,
means for shading a corresponding but- substan- '
This application is a continuation of my former
A iii
terial of low magnetic retentivity and compris
.
2. A synchronous alternating current motor
‘ combining a stator having an energizing winding
and providing a plurality of annularly spaced
pole pieces, a plurality of short-circuited rings
on one of said pieces progressively shading one
side portion thereof, means for shading a corre
_ spending side portion of another of said pole
tially smaller side portion of another of said
pieces, the remaining portions of the pole pieces
being unshaded, a rotor in the recess‘ de?ned by
the end faces of said pole pieces composed olf
magnetizable material of low magnetic reten?
tivity and including a central core and an odd
number of_ salient pole projections for each pair
of said pole pieces extending therefrom in an
nularly spaced relation, and a short-circuited 50
winding on said rotor.
‘
_
5. A synchronous alternating current motor
combining a. stator having two pole pieces which
are polarized oppositely when the stator is en
55
ergized, a short-circuited shading ring enclosing I
a side portion ofone of said pieces, a second
shading ring on said last mentioned piece en
)closing the same portion as said ?rst ring and an
additional adjacent section leaving one side of
the piece unshaded, means including a shading‘
‘ring enclosing a section of said other pole piece,
corresponding to but substantially greater in
area than the section enclosed by said ?rst men-__
tioned ring ‘for producing a substantially uni 65
formly shaded area on ‘said other pole piece, the
remainder of said other pole piece being un
shaded, means providing a magnetic path of low
reluctance between the unshaded area of said
second pole piece and the double shaded area. 01' 70
said ?rst pole piece and constituting an enlarge
ment of the unshaded face area of said second
pieces, producing a lesser degree of shading than
pole piece, ’ a synchronous rotor comprising a.
said rings, a rotor in the recess defined by said
central iron portion and a series of salient pole
statorpole pieces composed of magnetizable ma
projections extending therefrom greater in num- 75‘
6
2,105,866
her than the stator poles, and a squirrel cage
carried by said rotor.
6. A synchronous alternating current motor
combining a stator having pole pieces which are
polarized oppositely when the stator is enere
gized, shading means on one side of one of said
pieces enclosing the major portion of the piece
cross-section leaving the remaining side unshacl
ed, shading means enclosing a section of the
10 other pole piece to define shaded and unshaded
pole face areas corresponding approximately in
size to the areas de?ned by said first mentioned
shading means, a synchronous rotor comprising
a central iron portion and three equally spaced
15 salient pole projections extending therefrom for
each pair of stator pole pieces, a squirrel cage
carried by said rotor, and means providing a
magnetic path of low reluctance between the
unshaded area of said second pole piece and the
20 shaded side of said first pole piece and consti
toting an enlargement of the unshaded face area
of said second pole piece so as to completely over
lap one of said pole projections when the ad
jacent projection is disposed opposite the un
25 shaded area oi‘ said ?rst mentioned pole piece.
7. A synchronous alternating current motor
combining a stator having at least two pole pieces
de?ning a rotor recess and which are polarized
oppositely when the stator is energized, shading
30 means enclosing a side portion of one of said
pole pieces, shading means including a short-cir
cuited winding enclosing a side portion of said
other pole piece and having a resistance substan
tially greater than said ?rst mentioned means
35
for producing an unsymmetrical distribution of
shaded and unshaded fluxes about the rotor re
cess, and a rotor in said recess exposed to the
of
poles and having synchronous and
also induction motor characteristics.
8. A synchronous alternating current motor
comprising, in combination, a stator providing
two opposed pole pieces, a rotor composed of
material of low magnetic retentivity and com
prising a central core and three substantially
equally spaced and radially extending salient pole
projections exposed to the faces of said pole
pieces, short-circuited rings enclosing side por
tions of said pole pieces and shading the same
unequally, magnetic extensions of the unshaded
side tips of said pole pieces each following closely
50 around said rotor substantially uninterruptedly
to the shaded side of the adjacent pole piece
substantially less than the speed of said field,
and means on said rotor cooperating with said
field to produce induction motor action tending
to rotate said rotor at avspeed greater than said
synchronous speed, said shading means acting
differentially on said pieces whereby to render
said rotating ?eld unsymmetrical with respect to
the faces of at least one cooperating pair of said
pieces whereby to permit said synchronous speed
10
to be maintained.
11. A synchronous alternating current motor
combining a stator providing at least two pole
pieces having opposite polarity when the stator
is energized, shading means enclosing a major
portion of one pole piece and dividing the end
face thereof into an unshaded area and a larger
shaded area, shading means on the correspond
ing side of said other pole piece dividing the end
face thereof into an unshaded area and a shaded
area substantially smaller than said first men 20
tioned shaded area, and a rotor having three
equally spaced salient pole projections per pair
of stator poles having intervening non-magnetic
gaps between them substantially equal in cir
cumferential length to the e?ective circumfer
ential length of said unshaded area of said one
pole piece.
12. A synchronous alternating current motor
combining a stator providing a plurality of pole
pieces defining a rotor recess and annularly 30
spaced therearound, the adjacent poles being op
positely polarized upon energization of the stator,
means shading one side portion of one pole piece
and dividing the face thereof into an unshadecl
area and a shaded area substantially twice as
large, means shading the corresponding side por~
tion of another pole piece and dividing the face
thereof into a shaded area substantially equal
to said unshaded area and an unshaded area
substantially equal to said ?rst mentioned shaded 40
area, a rotor in said recess having three salient
pole projections for each pair of stator pole pieces
and intervening non-magnetic gaps, magnetic
extensions of the unshaded side tip of each pole
closely following the rotor contour and project
ing to the shaded side tip of the adjacent pole,
45
and a magnetic restriction interposed in the ex~
tension between the smaller shaded and un
shaded areas and acting to limit the effective
circumferential length of such unshaded area _
substantially to the length of one of said rotor
projections.
"
whereby, when one rotor pole projection is dis
13. A synchronous alternating current motor
posed opposite the unshaded section of one stator combining a stator providing at least two pole
pole face, an adjacent projection will be disposed ' pieces which are oppositely polarized when the
opposite the remotegend of the extension joined
to the unshaded section of the other pole piece.
9. A synchronous alternating current motor
comprising, in combination, a stator providing
a plurality of pole pieces, short-circuited rings
60 differentially shading the pole pieces which are
‘ oppositely polarized when said stator is excited
by alternating current, a rotor comprising a core
of magnetic material having three salient pole
projections for each pair of stator pole pieces,
65 and means on said rotor acting to create induc
stator is excited, means,shadingvcorresponding
side portions'of said pole‘ pieces and dividing, '
the faces thereof into unshaded and‘ shaded
areas, a. rotor composed of magnetizable mate
rial of low magnetic ret'entivity and having 60
salient pole projections greater‘ in number than
the number of said pieces and separated by in
tervening segmental gaps of substantial lengths
and a magnetic extension of the unshaded side
tip of one of said pole pieces closely following 65
the rotor contour, said unshaded and shaded
tion motor torque when the stator is excited.
areas 01' the two pole pieces being proportioned
l0. A synchronous alternating current motor
combining a stator having a plurality of pole
and spaced relative to each other so that two of
pieces de?ning a rotor recess and having shading
70 means thereon acting, when the stator is excited,
to cause shifting of .the magnetic field around
sion and the adjacent unshaded area when
another projection is opposite the unshaded area
said recess, a rotor in said recess having salient
projections greater in number than the stator
poles whereby to establish a synchronous speed
said projections will be exposed to said exten
of the other stator pole.
14. A synchronous alternating current motor
combining a rotor composed of magnetizable ma
terial of low magnetic retentivity and having a
aioacce
7
plurality of radially disposed salient pole projec
plurality of annularly spaced pole pieces, sub
tlons separated by segmental non~magnetic gaps,
a stator providing at least two pole pieces having
stantially closed magnetic connections between
the adjacent side tips of the adjacent pole pieces
end faces providing a substantially continuous
surface overlapping three of said projections and
three of said gaps, and means shading .corre
sponding side portions of said pole pieces and
de?ning unshaded areas of di?‘erent sizes on said
surface, the area on the face of one pole over~
10 lapping two of said rotor projections when an
other rotor projection is opposite the unshaded
area of the other stator pole.
15. A synchronous motor having, in combina
tion, a stator having afplurality of pole pieces
de?ning a rotor recess and adapted to be ener
cooperating with the faces thereof to de?ne a
substantially continuous cylindrical iron surface,
means shading corresponding side portions of
said pole pieces, a rotor within said surface com
posed of magnetizable material of low magnetic
retentivity and having a plurality of annularly
spaced salient pole projections greater in number 10
than the number of said pole pieces, whereby
to establish a sub-synchronous operating speed
of said rotor, a squirrel cage winding on said
rotor cooperating with said stator to produce in
duction motor torque su?icient to initiate rota 15
gized by alternating current, shading means op
tion of said rotor and accelerate the same to
erating to cause shifting of» the magnetic field
around said recess when the stator is energized,
said sub-synchronous speed, and annularly spaced
magnetic restrictions in said stator confining the
a rotor in said recess composed of magnetizable
26? material of low magnetic retentivity and com~
prising a core with a plurality of salient pole
projections spaced apart a distance approximate~
1y equal to their circumferential length, and a
squirrel cage Winding on said core in which cur
.?ow of unshaded ?ui; from the stator into the
rotor through an intervening pole face area span 20
hing only one of said rotor projections.
19. A sub-synchronous motor having, in com
bination, a stator adapted to be energized by
alternating current and having a plurality of
rents are induced to produce induction motor, annularly spaced pole pieces, short-circuited 25
action, there being three of said salient rotor coils of low resistance heavily shading corre
poles for each pair of stator poles whereby to sponding side portions of said pole pieces, a rotor
establish a sub-synchronous operating speed between the faces of said pole pieces composed
nearest the speed at which the motor operates of ‘magnetizable material of low magnetic reten
3d most ef?ciently as an induction motor.
tivity and having a plurality of salient pole pro 30
16. A sub-synchronous motor having, in com
jections, extensions of the unshaded side tips
bination, a stator having a plurality of pole pieces of said pole pieces following the rotor contour
de?ning a rotor recess and adapted to be ener
and providing substantially closed magnetic con
gized by alternating current, shading means op
erating to cause shifting of the magnetic field
around said recess when the stator is energized,
nections between the adjacent pole pieces, said
rotor pole projections being sui?cient in number 35
relative to the number of pole pieces and spaced
and a rotor in said recess composed of magne
apart surhcient ‘ distances to establish a sub
tizable material having low magnetic retentivity. synchronous operating speed of at least one-half
and comprising a core with three salient pole
40 projections for each pair of stator pole pieces,
said projections being of substantially equal cir
cumferential lengths separated by intervening
norpmagnetic gaps each having a circumferen
tial length at least equal to one-fourth of the
45 rotor pole pitch, the number of said projections
of the true synchronous speed of the motor, and
said stator being constructed to provide a single 40
low reluctance ?ux path through the rotor ex
tending through the unshaded face area of one
of said pole pieces and a single rotor projection
‘in register therewith, and a squirrel cage winding
on said rotor cooperating with said pole pieces, 45
being greater than the number of said pole pieces said shading means and said extensions to pro
whereby to establish a predetermined sub-syn
duce strong induction motor action capable of
chronous operating speed equal to two-thirds of starting and accelerating said rotor to said sub
the true synchronous speed, and a squirrel cage” synchronous speed.
_
winding on said core in which currents are in
20., A sub-synchronous alternating current
duced to produce induction motor torque capable motor. having, in combination, an even number
of initiating rotation of said rotor and acceler
of annularly spaced pole pieces, shading means
ating the same to said sub-synchronous speed.
enclosing corresponding side portions of said pole
17. A sub-synchronous motor having, in com» pieces, a rotor between said poles composed of
bination, a stator having 2N pole pieces de?ning magnetizable material of low magnetic reten
a rotor recess and adapted to be energized by tivity and having an oddynumber of annularly 1
alternating current, shading means on said pole spaced salient pole projections for each pair of
pieces operating to cause shifting of the mag ' stator pole pieces greater than the number of
netic field around said recess, a rotor in said
said pole pieces, and a short-circuited ‘winding
60 recess composed of magnetizable material of low
on said rotor cooperating with said stator to
magnetic retentivity, said rotor being provided produce induction motor torque, the areas of
with means including 3N equally ‘spaced salient said side portions on the adjacent pole pieces
pole projections on said rotor composed of low being of different widths whereby one of said
retentivity material and cooperating with said projections will be disposed opposite the unshaded
stator for establishing a sub-synchronous oper
face area of one pole piece when another ‘of the
atlng speed of said rotor equal to two-thirds of projections is disposed opposite the unshaded face
the true synchronous speed as determined by area of the adjacent pole piece.
the number of stator poles, and a winding on
21. A sub-synchronous alternating current
said rotor in which currents are induced by the motor having, in combination, an even number
70 stator ?eld, said stator and said rotor cooper
of annularly spaced pole pieces, short-circuited 70
ating to produce induction motor torque capable coils shading corresponding side portions of said
of initiating rotation of the rotor and acceler
pole pieces, a rotor invthe recess de?ned by the
ating the same to said sub-synchronous speed.
- faces of said pole pieces composed of magnetizable
18. A sub-synchronous alternating current mo
material of low magnetic retentivity and having
75 tor having, in combination, a stator having‘ a an odd number of salient pole projections for 76
'8
aromas
each pair of said pole piece'sgreater than the
24. A self-starting subsynchronous motor com
number of said pole pieces and each correspond
prising, in combination, a stator unit having a
ing in circumferential length approximately to
the e?ective unshaded face area of one of said
(Fl pole pieces, a short-circuited winding on said
rotor cooperating with said stator to produce
induction motor action, and a magnetic exten
sion of the unshaded side tip of 'the adjacent
plurality of annularly disposed pole pieces, means
for shading corresponding side portions of said
pole pieces, a rotor unit having a' plurality of
salient pole projections cooperating with the pole
pieces of said stator unit, said projections being,
area.
greater in number than said pole pieces, at least
one of the pole pieces of said stator unit having
an unshaded portion of substantially greater cir 10
cumferential length than said rotor projections
and cooperating with successive rotor projections
22. A sub-synchronous alternating current
motor having, in combination, a stator having
to form a mobile ?ux path therebetween as the
rotor projections move across the same, another
pole piece spanning substantially the entire area
10 of one of said projections when the adjacent
projection is disposed opposite said unshaded iace
15 a plurality of annularly spaced pole pieces with
faces defining a rotor recess, a. rotor between
said poles composed of magnetizable material
of low magnetic retentivity and having annu
larly spaced salient pole projections greater in
number than the number of said pole pieces, a
short-circuited winding on said rotor cooperating
with said stator to produce induction motor ac
tion, means shading corresponding side portions
of said stator pole pieces, and magnetic restric
tions separating the shaded and unshaded face
areas of said pole pieces and de?ning an un
shaded .iace area on one pole piece substan
tially equal in circumferential length to the cir
cumferential length of one of said projections,
and an unshaded area on the adjacent pole piece
of substantially different circumferential length
than said first mentioned unshaded area and dis
posed opposite one rotor projection when another
rotor projection is in registry with said ?rst
35 mentioned unshaded area.
23. A self-starting subsynchronous motor com~
prising, in combination, a stator unit having a
pluraity of annularly disposed pole pieces, means
for shading corresponding side portions of said
pole pieces, a rotor unit having a plurality of
salient pole projections cooperating with the pole
pieces of said stator unit, said projections being
of said stator pole pieces having an unshaded 15
portion of substantially the same circumferential
length as said rotor projections and cooperating
with successive rotor projections to form a sub
stantially ?xed ?ux path therebetween as the
20
rotor projections cross the same.
25. A sub-synchronous alternating current mo
tor having, in combination, a stator having a
plurality of annularly spaced pole pieces, sub
stantially closed magnetic connections between
the adjacent side tips of the adjacent pole pieces
cooperating with the faces thereof to de?ne a
substantially continuous cylindrical iron surface,
means shading corresponding side portions of
said pole pieces, a rotor within said surface com
posed of magnetizable material of low magnetic 30
retentivity and having a plurality ,of annularly
spaced salient pole projections greater in number
than the number of said pole pieces, whereby to
establish a sub-synchronous operating speed of
said rotor, a squirrel cage winding on said rotor 35
cooperating with said stator to produce induction
motor torque su?icient to initiate rotation of said
rotor and accelerate the same to said sub-syn
chronous speed, and means for con?ning the ?ow
of unshaded ?ux to the rotor to unsymmetrically 40
arranged areas of said cylindrical iron surface.
26. A sub-synchronous alternating current mo
tor including, in combination, a stator having at
least two pole pieces de?ning a rotor recess which
are polarized oppositely when the stator is ener
gized, means for producing a different geomet
rical distribution of shaded and unshaded ?ux
greater in numberthan said pole pieces, at least
one oi the pole pieces of said‘stator unit having
45 an unshaded portion of major facial extent in a
direction circumferentially of the rotor as com
pared to the salient projections of said rotor unit
which are of minor facial extent, the said major across the face of one pole piece than across the
extent and minor extent pole piece portion and ' opposite‘ pole face including shading means en 50
closing corresponding side portions of said pole
projections being proportioned relative to each
other to provide a magnetic path free of major
variations at substantially all positions of‘ rela
tive movement therebetween, another of said
stator unit pole pieces also having an unshaded
55 portion of smaller facial extent than said major
extent pole piece cooperating with said rotor to
provide a flux path therebetween which varies
widely in reluctance to produce a synchronous
torque on said rotor.
pieces, a- rotor in said recess exposed to the faces
of said poles, and means including a. plurality of
salient pole projections on said rotor for pro;
ducing a sub-synchronous characteristic therein,
said salient pole projections being greater in
number than said pole pieces.
EDGAR D. LILJA.
~
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